But privacy rights groups counter the state's "trust us" promise not to abuse the technology does not ease their concerns that someone's biological makeup could soon be applied for a variety of non-criminal purposes.

The justices raised a host of hypotheticals in their spirited oral arguments, laying out two sharply divided scenarios.

"There is something inherently dangerous about DNA collection that is not the same as fingerprinting," said Justice Sonia Sotomayor. "How far do we let the state go each time it has some form of custody over you in schools, in workplaces, wherever else the state has control over your person?"

"This is what is at stake: Lots of murders, lots of rapes that can be solved using this new technology that involves a very minimal intrusion on personal privacy," said Justice Samuel Alito. "Why isn't this the fingerprinting of the 21st century? What is the difference?"

Twenty-six states and the federal government allow genetic swabs to be taken after a felony arrest and without a warrant.

Each has different procedures, but in all cases, only a profile is created. About 13 individual markers of some 3 billion are isolated from a suspect's DNA. That selective information does not reveal the full genetic makeup of a person, and officials stress, nothing is shared with any other public or private party, including any medical diagnostics.

The Obama administration has signaled its support.

The case involves a Maryland man convicted of a 2003 rape in Wicomico County in the state's Eastern Shore region. Alonzo King Jr. had been arrested four years ago on an unrelated assault charge, and a biological sample was automatically obtained at that time. That sample was linked to the earlier sexual assault.

King moved to suppress that evidence on Fourth Amendment grounds, but was ultimately convicted of the 2003 first-degree rape offense and was given a life sentence. Both King and his legal team turned down CNN's request for an interview.

A divided Maryland Court of Appeals later agreed with King, saying suspects under arrest enjoy a higher level of privacy than a convicted felon, outweighing the state's law enforcement interests. That court also said obtaining King's DNA immediately after arrest was not necessary in identifying him, and that the process was more personally invasive than standard fingerprinting.

The Fourth Amendment grants the "right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures."

The issue of citizen privacy has been particularly acute since the 9/11 attacks. Federal and state governments have stepped up surveillance of suspected terrorists and their allies and high-risk targets, like government buildings and shopping malls.

The current conservative majority court has generally been supportive of law enforcement in recent search and privacy disputes, but not always. The court last year ruled police could not place a GPS tracking device on a drug suspect's car for several weeks, without first obtaining a search warrant.

Chief Justice John Roberts last July allowed the Maryland DNA law to stay in effect until a full appeal could be filed. The high court then agree to decide the constitutional issues. Roberts at the time hinted his tentative support, but in arguments he was tough on both sides.

"There's no reason you couldn't undertake this procedure with respect to anybody pulled over for a [misdemeanor] traffic violation?" he asked with some concern, to state attorney Katherine Winfree. She said Maryland's law in three years produced 225 matches, 75 prosecutions and 42 convictions.

Scalia said that catching bad guys is a "good thing, but the Fourth Amendment sometimes stands in the way."

Other members of the bench were equally skeptical.

Justice Ruth Bader Ginsburg: "This is very reliable tool, but it's not based on any kind of suspicion of the individual who's being subjected to it, right?"

Justice Elena Kagan: "Just because you've been arrested, doesn't mean that you lose the privacy expectations and things you have that aren't related to the offense that you've been arrested for. .. If it's just to solve cold cases, which is the way you started, then it's just like searching your house, to see what's in your house that could help to solve a cold case."

But there was a measure of support for the state's efforts.

Justice Stephen Breyer: "I can argue that it is certainly a much lesser intrusion than fingerprints. You have to stand there, have the thing rolled; stick out your tongue. I mean, it's hard to say it's more for me. Accuracy: it's much more accurate."

Justice Anthony Kennedy: "My question is whether or not the police who have John Doe in custody for a felony have an interest in knowing at the outset or within a few weeks time whether or not that person has committed other crimes?"

Roberts again: "Doesn't that sound just like a Breathalyzer? You are pulled over, they [police] say, we want you to take a Breathalyzer test. They say, you don't have to, but if you don't your license is suspended for six months or whatever. Why isn't that the same thing?"

A 1994 federal law created a national database in which local, state, and federal law enforcement agencies can compare and share information on DNA matches from convicted felons, but courts have been at odds on just when such samples can be collected and the information distributed.

The state DNA collection law in Maryland is set to expire at the end of the year, but the justices are likely to decide its constitutionality before then.

In a brief filed by 49 states supporting Maryland, officials also say the information is secure, and retested when an initial "hit" is identified. After a warrant is issued for probable cause, another fresh DNA sample is taken and it is that test that is used to ultimately prosecute in court. Each initial test costs about $30.

The Fourth Amendment requires the government to balance legitimate law enforcement interests with the privacy rights of individuals. A key area of concern in the high court was whether developing "Rapid DNA" technology will allow initial identification testing to be completed within about two hours. Currently it can take two weeks or more, depending on backlogs.

In responding to concerns DNA testing after arrest had only one real purpose—to solve unrelated, past crimes-- the state said quick testing of DNA could serve another purpose. Winfree said similar to fingerprints, the new technology could help determine whether arrested suspects should be released on bail, or remain in jail because of other newly suspected past offenses. She cited an FBI estimate the new technology could in place within 18 months.

King's attorney, Kannon Shanmugam, told the high court, "There are over 12 million arrests in the United States every year. Virtually all of the arguments advanced by [Maryland] and the United States would justify the blanket collection and retention of DNA from ordinary citizens."

And civil liberties groups worry inadequate testing by overwhelmed lab technicians can lead to errors, such as the one that sent Dwayne Jackson to prison for armed robbery. It was three years before a lab mistake was noticed, and the Nevada man was freed as an innocent man.

Deoxyribonucleic acid is a coded molecule providing a genetic map for the development of all known living organisms. By 2000, all 50 states and the federal government required DNA collection from convicted offenders, and was soon expanded by many jurisdiction to criminal arrests.

The number of offender profiles in federal Combined DNA Index System (CODIS) is now about 10 million, with more than a million arrestee profiles.

Congress in December passed the Katie Sepich Enhanced DNA Collection Act, a grant program to help states pay for the expanded system. The 22-year-old woman was murdered in 2003, but her killer was not identified until three years later, after his conviction for another crime, when his DNA matched cold-case evidence under the victim's fingernails.